This invention relates to a device for unlocking the door of a motor vehicle or the like, and more particularly to a door unlocking device having a door unlocking mechanism which automatically unlocks a door in response to a signal which the user transmits through a signal transmitter or the like.
Recently some motor vehicles have been equipped with a so-called wireless door lock device which is designed for instance as follows: An ignition key is provided with a signal transmitter. The transmitter is operated by the operator to transmit a radio wave signal (propagating in the air), which is detected by received signal discriminating means provided on the vehicle body. When it is determined that the radio wave signal is the one predetermined for the door of the motor vehicle, an electric actuator is operated to automatically lock or unlock the door.
In general, the transmitter is operated on a battery. When, the transmitter being used for a long time, the power of the battery is consumed up, it becomes impossible to operate the transmitter to transmit the radio wave signal; that is, it becomes impossible to unlock the door.
In another example of the conventional door unlocking device, an ignition key has a number of small holes, and a light emitting and receiving device is provided on the side of the key cylinder. When the ignition key is inserted into the key cylinder, light passed through the small holes of the ignition key is utilized to output a signal. When it is determined that the signal is the one predetermined for unlocking the door, the door lock is opened. However, the door unlocking device is still disadvantageous in that, when the device is used for a long time, the small holes of the ignition key may be deformed or collapsed, so that the predetermined signal cannot be provided; that is, the door cannot be unlocked.